Molding machines include hot runner nozzles that define a melt channel for passing molten material to a desired location such as a mold cavity. It is important that the molten material be kept at a desired temperature to ensure that it flows and cures properly. Typically, hot runner nozzles are heated with a resistance heater that is wound about the outer surface of the nozzle body. A thermocouple is disposed within the nozzle body to sense the body temperature and the resistance heater is operated by a control system to maintain the body at a desired temperature.
A problem with such conventional nozzles is that the temperature within the nozzle varies over the length of the nozzle body. Usually, the ends of the nozzle tend to be much cooler than the middle portion of the nozzle due to heat loses occurring at the ends. As a result, it is difficult to maintain the melt within the melt channel at a constant desired temperature. This is problematic in particular for molten materials that are sensitive to minor changes in temperature. If the temperature is increased too much then the melt will burn in the middle portion of the nozzle, and if the temperature is decreased to avoid burning then the melt might have flow problems or other problems that will effect its ability to cure properly within the mold cavities.
There is a need for an apparatus to heat the melt channel within a nozzle body to a desired temperature that remains relatively constant over the length of the nozzle.